Brain Machines

Hi,
I'm very interested in mind machines. I'd like to buy one to relax, but
also to evoke altered states of consciousness.
Although I tried a David Paradise a few times and it did relax me, I
still doubt whether all the promises the manufacturers make are true.
What is your experience with these machines, if you have any? What kind
of a machine do you use (make, model)?
I'd like to buy the best mind machine there is (which is not by
definition the most expensive), but here in Belgium, where I live, there
are virtually no mind machines on the market (David's the only one, I
guess). I must order directly from the States or the UK, so I can't
check them out.
If you can help me, either by sharing your own experiences or by
referring to interesting sources, please email me.
Thanks a lot,
Johan